The present invention relates to staplers and, more specifically, to heavy-duty staplers.
Heavy duty staplers typically include a base, a cartridge assembly pivotally mounted to the base, and a lever assembly including a lever arm that will provide a force to the cartridge assembly to drive a staple through a stack of sheets. The lever arm is commonly pivotally mounted to either the cartridge assembly or the base.
There are many characteristics of a heavy-duty stapler that define the quality of the stapler. For example, one important characteristic is the stapler""s ability to consistently drive a staple through a thick stack of sheets without staple failure and without jamming the magazine. Another characteristic is the amount of force required to use the stapler. It can be appreciated that it would be desirable to produce a stapler that can consistently drive staples through a stack of sheets without failure and with a reduced force applied to the lever arm.
The present invention provides a stapler that is designed to require less force on the lever arm in order to drive a staple through a stack of sheets. This is accomplished by the relative positioning between the pivot points of the cartridge assembly and lever assembly, and the connection between the cartridge assembly and the lever assembly.
More specifically, the present invention provides a stapler comprising a base defining a horizontal plane, a cartridge assembly coupled to the base at a cartridge attachment point, the cartridge assembly including a ram, and a lever arm pivotally coupled to the base at a lever pivot axis. The lever arm includes a grip at one end for receiving a manual input from a user, and the lever arm is coupled to the ram at a ram input in order to provide a drive force. The stapler includes an inherent force factor, calculated as the horizontal distance from the lever pivot axis to the end of the lever arm divided by the horizontal distance from the lever pivot axis to the ram input, of is at least 3.8 (preferably at least 3.9).
In one embodiment, the cartridge assembly includes a cartridge housing, and the ram is slidable relative to the cartridge housing along a ram axis. In the static position, the lever arm defines an effective lever axis that is at least about 65xc2x0 (preferably at least about 70xc2x0 and most preferably about 72.4xc2x0) offset from the ram axis. When stapling, the effective lever axis is greater than about 95xc2x0 (preferably at least about 100xc2x0 and most preferably about 103xc2x0) when the lever arm is compressed to the fully stapled position.